1. Field of the Invention
The invention relates to a process for opto-electronic inspection of bottles, and more particularly to a process for inspection of portions of bottles such as sealing rims and/or threads.
2. Description of the Related Art
In a known opto-electronic inspection system according to DE- No. 3,228,464, the disclosure of which is incorporated herein, the side walls of cleaned glass bottles are inspected for residual impurities by moving each bottle on a circular path through a beam between a diffuse source of light and an electronic image converter and simultaneously rotating said bottle 360.degree. with respect to its longitudinal axis for development of its entire side wall. The image converter, which consists of a photodiode camera and a scanner (rotating mirror), follows the advance motion of the bottle synchronously and is continuously aligned with the longitudinal axis of the bottle tested. Each scanning signal of the image converter generated in a defined angular rotating position of the bottle represents a sequence of image points located above each other (line of light) and constitutes an image of two radially opposing partial surfaces of the side wall of the bottle. Any contamination of the side wall causes a break in the intensity of the scanning signal at the point in the signal generated by the photodiodes in the row located in the beam path through the impurity which otherwise is practically constant. To determine the presence of an impurity, it is merely necessary to compare the intensity level of every scanning signal with a minimum level, wherein any signal below the minimum level identifies a break in the intensity and thus an impurity. In place of a row of diodes and a scanner following the bottle moving on a circular path, more recently an array of diodes has been used. The array consists of a plurality of adjacent rows of photodiodes, the width whereof covers the entire range of observation.
The known side wall inspector is not capable of observing or inspecting the mouth area of a glass bottle. This mouth area includes the annular surface around the mouth of the bottle serving as the tightening surface for both crown cork and screw cap closures. In bottles exhibiting thread closures, for example mineral water bottles, the mouth area also includes the bottle thread. Large chips of the glass in the annular sealing surface or the bottle thread interferes with the normal closing of the bottle, therefore it is important to separate bottles with such chips prior to the filling process. Known mouth inspection devices which produce a television image of a view of the mouth are only able to inspect the sealing surface, not the bottle thread. However, even the inspection of the sealing surface is inaccurate due to inadequate defect resolution because only the light reflected by the bottle mouth resulting from the necessary illumination from above impacts the optics of the television camera. This light is of insufficient intensity to enable measuring detection of intensity differences produced by chipped glass.